As aircraft become an increasingly more important mode of transportation, efforts continue to increase the efficiency, safety, and comfort of air travel. In propeller driven aircraft, the propulsion system, and especially the propellers, are under constant engineering scrutiny in order to continuously improve efficiency and safety, while reducing vibration and noise associated with the propulsion system.
Various altitude-compensating propeller pitch controls and constant-speed propeller pitch controls have been known since the 1930's. The constant speed propeller, in which the pilot manually selects the desired rotation rate and the pitch control mechanism controls the blade pitch to maintain that rotation rate, is still the standard on high-performance private and small commercial aircraft.
U.S. Pat. No. 5,209,640 discloses a computer-controlled pitch controller in which flight speed, atmospheric pressure, atmospheric temperature, and throttle setting are considered to calculate an optimum rotation rate for propeller efficiency.
At high power output, aircraft propeller tips frequently approach the speed of sound, causing loss of efficiency and high noise due to compressibility effects. Noise in particular is a major problem during takeoff because of the noise sensitivity of communities near airports.